1. Field of the Invention
The invention relates to a railway car truck incorporating a novel interconnection between the wheel set and side frame.
2. Description of the Related Art
The conventional railway car truck in use in North America for several decades has been the three-piece truck, comprising a pair of parallel side frames connected by a transversely mounted bolster. The bolster is supported on the side frames by spring sets. The wheelsets of the truck are received in bearing adapters placed in leading and trailing pedestal jaws in the side frame, so that axles of the wheelsets are parallel. The bearing adapters permit slight angular adjustment of the axles. The railway car is mounted on the center plate of the bolster, which allows the truck to pivot with respect to the car. The spring sets permit the side frames to move somewhat with respect to the bolster, about the longitudinal, vertical, and transverse axes.
On straight track, a three piece truck with parallel side frames and parallel axles perpendicular to the side frames (i.e., a perfectly “square” truck) rolls without inducing lateral forces between the wheel flange and the rail. However, at high speeds, minor perturbations in the track or in the equipment can lead to a condition known as “hunting,” which describes an oscillating lateral movement of the wheelsets that causes the railcar to move side-to-side on the track. Hunting may be dangerous when the oscillations attain a resonant frequency. A number of causes are implicated in hunting, and a number of solutions have been proposed in the prior art to raise the “hunting threshold,” but the condition is generally thought to be improved by increasing the rigidity of the truck.
Curved track poses a different set of challenges for the standard three-piece truck. When a railway car truck encounters a turn, the distance traversed by the wheels on the outside of the curve is greater than the distance traversed by wheels on the inside of the curve, resulting in lateral and longitudinal forces between the wheel and the rail. These wheel forces cause the wheel set to turn in a direction opposing the turn. On trucks with insufficient rigidity this results in a condition variously known as “warping,” “parallelogramming” or “lozenging,” wherein the side frames remain parallel, but one side frame moves forward with respect to the other. The “lozenging” condition can cause increased wear on the track and equipment, increase rolling resistance, and if severe enough result in a derailment.
In order to provide the standard three-piece truck with the ability to negotiate turns, the truck is generally designed to allow a nonparallel condition of the axles during the turn, which is then recovered on straight track. This may be achieved by permitting relative movement of the bearing adapters within the pedestal jaws of the side frames.
For the purposes herein, a “bearing adapter” is a piece which fits in a pedestal jaw of a side frame. One side of the bearing adapter is curved for engagement with the roller bearing of the axle and the other side fits in the pedestal jaw. Typically, a thrust lug protrudes from the vertical side wall of the pedestal jaw, and mates with a slot on the bearing adapter to maintain the bearing adapter in place and provide limits on the range of relative movement between the bearing adapter and pedestal jaw.
In order to improve curving performance, it is known to interpose an elastomeric bearing member between the side frame and the tops of the bearing adapters. The elastomeric member permits the side frames to maintain a ninety degree relationship with the wheelsets on straight track, while on curved track allowing the wheelsets some freedom of movement to depart from a square relationship to respond to turning forces and accommodate the nonparallel condition of the axles. The elasticity of the member biases the truck to return to its square position. Various systems to securely attach elastomeric pads to the side frame pedestal jaw are described in the prior art, including U.S. Pat. No. 4,674,412, which also contains a description of the prior art related to elastomeric pads generally.
The prior art is also replete with systems for maintaining the bearing adapter securely in place in the pedestal jaw. U.S. Pat. No. 5,503,084, for example, describes a truck having a system for holding the bearing adapter in position within the pedestal jaw using tie rods running through a bore in the bearing adapter to prevent the bearing adapters from rotationally moving.
A further mechanism to permit a truck to negotiate a turn is known as a “steerable” truck, which is generally a truck that allows rotation of each wheelset about its vertical axis so that the wheelsets may take an out-of-square position with respect to a longitudinal axis of the truck. In a steerable truck, the wheelsets are joined by an arm which controls and maintains the relationship between the wheelsets. The arm is further connected to a body of the railroad car so that movement between the car body and the wheelsets is maintained in a fixed relationship. An exemplary steerable truck is disclosed in U.S. Pat. No. 3,789,770. The invention described herein may be used with steerable and non-steerable trucks.
None of the above-described prior art recognized the advantage of an interconnection providing increased stiffness in a longitudinal direction relative to a reduced spring rate laterally between the side frame and the bearing adapter to improve passive steering and reduce lozenging.
These and other objects of the invention may be achieved by various means, as described in connection with the following description of the preferred embodiments.